RFID systems are well known and include passive and active RFID tags along with associated communications equipment and control systems. Each tag typically includes information that at least identifies the tag uniquely in some universe of tags. In the simplest systems, each sensor detects those tags that are within range and communicates the tag identities, and possibly other information such as a sensor reading timestamp, to a control system that then initiates an appropriate response. Details of the operation of RFID systems are well known in the art and further description is not believed necessary for an understanding of the subject invention.
More complex RFID systems locate tags more precisely by measuring the distance from sensors to tags or by triangulation. Other systems such as active badge systems sense tags using different technology such as infrared radiation or ultrasonic sound. As used herein the terms RFID tag and RFID system are intended to include such tags and systems unless otherwise indicated.
RFID systems have proven very successful. They are used in security systems such as corporate ID badges that provide access in buildings. Additionally, they have proven of great value in inventory control applications and are excellent systems for tracking what comes into and what comes out of a warehouse. Furthermore, the well-known EZ Pass® system uses RFID systems at tollbooths to read tags affixed to vehicles and charge tolls to corresponding accounts. Furthermore, responsive environment systems using RFID tags have been described such as the Pitney Bowes ATIRA responsive environment. However, RFID systems are limited in that sensors have limited in range and do not function reliably through walls or other barriers or partitions. Thus in many cases the sensors provide only probabilistic observations of the state. For example, a sensor located at the entrance to a room may be unable to distinguish among tags entering the room, tags leaving the room, and tags passing by the entrance.
Thus it is an object of the subject invention to provide a method and system for predicting, recording and tracking real world states in an RFID system based upon sensor observations such as probabilistic observations of RFID tags.